Lesson 3: Astronomy after Copernicus
New Heavens--the rise of the telescope
Try going outside at night and looking at the sky. Although night skies were darker most places in the early modern world due to the lack of artificial lighting, what you are seeing is basically what ancient, medieval and Renaissance astronomers had to go on as far as data. They were "naked-eye" astronomers.
Some, most notably Tycho, could achieve remarkable precision with the naked eye, but they were limited to what they could see. Ironically, Tycho’s painstakingly gathered observations soon beaome obsolete due to the most important technological change in the history of astronomy, the invention and rise of the telescope.
The earliest recorded telescope combining a convex and concave lens in a tube was in the Netherlands in 1608. The principle of the telescope was so simple that much of its early spread was not caused by the physical introduction of telescopes, but people hearing about telescopes and constructing their own.
The greatest technical innovator of the early telescope, however, was Kepler. He devised the so-called “astronomical” telescope, combining two convex lenses and obtaining greater accuracy of observation at the price of turning the image upside-down, as described in his Dioptrice (1611). This is one of the few innovations in telescope design in this period based on optical theory rather than tinkering, and it took a while for it to be accepted.
The first person to demonstrate the telescope’s astronomical possibilities was the Italian professor Galileo Galilei, who built his own telescope after hearing about Dutch telescopes. Galileo’s telescopes, with a magnification of 30 diameters, were the most powerful of their time; so powerful that they made his observations difficult to duplicate.
It was the telescope that made Galileo an astronomer. He had been a mathematician and physical theorist, known in Italian learned circles for his radical disdain for Aristotelian physics. Galileo had little interest in the painstaking accumulation of precise observations of the stars and planets which lay at the heart of traditional European astronomy. He used his telescope to poke around in the sky and find new things, and there was a world of riches for him to explore.
Galileo observed the moons of Jupiter (the first satellites of a planet - other than the Moon - known), as well as the mountains of the Moon itself, the phases of Venus, and the composition of the Milky Way out of innumerable stars. These epochal discoveries, which Galileo interpreted as supporting the Copernican system, were announced in 1610 in The Starry Messenger(1610).
The telescope also made Galileo one of Europe’s first scientific celebrities, enabling him to leave his job as a professor at the University of Padua (Europe’s leading scientific university) and enter the court of the Duke of Tuscany. He even named the moons of Jupiter after the Medici family of the Duke. Shapin discusses the impact of some of Galileo’s observations on pages 15-20.
Telescopes were controversial. They were the first radical extension of the human senses, and many viewed the images they produced with suspicion. After all, there was no way of checking what a telescope revealed except by using another telescope.
Telescopes made the hitherto neglected study of lenses a vital part of optics. They made clear to astronomers the relative closeness of the planets in space and their relative similarity to the earth as opposed to the unimaginable number, distance and difference of the stars.
